1. Field of the Invention
This invention relates to a process for the epoxidation of olefinically unsaturated hydrocarbon compounds with peracetic acid formed by the catalytic reaction between hydrogen peroxide and acetic acid. The process of the present invention is particularly suitable for epoxidating terminally and/or internally olefinically unsaturated hydrocarbon compounds which are liquid under normal (atmospheric) pressure at a temperature within the range of about 50.degree. to 100.degree. C.
2. Description of Related Art
The epoxidation of unsaturated fatty acid derivatives, primarily soya oil, is carried out industrially on a large scale. The epoxidized product comprises a PVC compatible plasticizer. The product simultaneously acts as a heat stabilizer in PVC. Epoxidized soya oil also has been approved as an additive for plastics used with foods.
In current commerical practice, performic acid is still used as the epoxidizing agent. The performic acid is obtained in situ by reaction between formic acid and hydrogen peroxide. Even so, unsatisfactory yields of epoxide product generally are obtained with performic acid in epoxidation processes involving alpha-olefins and unsaturated fatty alcohols. Unfortunately, it is not possible, based on safety considerations, to overcome this problem simply by increasing the concentrations of hydrogen peroxide and formic acid in the reaction mixture.
The rate of formation of the corresponding peracid by reaction between acetic acid and hydrogen peroxide is comparatively slow. However, the velocity of the epoxidation reaction using peracetic acid as the epoxidizing agent appears higher than where performic acid is used. Another potential advantage of using peracetic acid for expoxidation relative to performic acid is the greater stability of peracetic acid. In fact, peracetic acid may be formed on an industrial scale outside the epoxidation reactor with greater safety and with fewer decomposition losses than can performic acid.
It also is known that acetic acid and hydrogen peroxide can be reacted to form peracetic acid in the presence of strongly acidic cation exchange resins, based for example on polystyrene. Particularly suitable catalyst resins are gel-like and/or macroporous resins containing sulfonic acid residues as ion exchange groups. In this connection, reference is made, for example, to H. K. Latourette et al., J. Am. Oil Chem. S.: 37 (1960), pages 559 to 563; to R. J. Gall et al., J. Am. Oil Chem. S.: 34 (1957), pages 161 to 164 and to the literature cited therein. Ion exchange resins marketed under the tradenames Amberlite IR-120 by Rohm & Haas Co.; Chempro C-20; Dowex 50X by the Dow Chemical Co. and other equivalent resins are mentioned in these references as suitable ion exchange resin catalysts.
In particular, it is taught that peracetic acid is formed in situ by passing the hydrocarbon starting material to be epoxidized together with hydrogen peroxide and acetic acid over the heterogeneous solid resin catalyst. Alternatively, the various reactants are agitated together with the resin catalyst in a stirred reactor. However, these methods of carrying out the epoxidation reaction have serious disadvantages in terms of industrial application. For example, the unsaturated hydrocarbon compound normally wets the catalyst surface, thus blocking its pores and resulting in rapid deactivation of the resin catalyst for the production of peracetic acid. In the stirred-reactor embodiment, the catalyst particles tend to be mechanically abraded thus accelerating the above-described effect.
Because the epoxidation reaction generally requires a temperature above about 50.degree. C., for example up to about 80.degree. C., the thermal load on the resin catalyst in these arrangements also is comparatively high. Finally, rapid swelling and, in some cases, even partial dissolution of the ion exchange resin catalyst is observed under the effect of the highly active components, namely H.sub.2 O.sub.2 and the epoxide product.
Another major difficulty generally affecting epoxidation reactions involves temperature control in the epoxidation reactor. It is known that considerable heat is generated during epoxide formation. This heat must be rapidly dissipated from the reaction mixture in order to avoid the harmful consequences accompanying an excessive temperature increase. Since it is desired to avoid excessive agitation of the reaction mixture which would otherwise tend to improve heat transfer, this problem generally imposes serious process limitations. For example, in the case of an externally cooled column reactor, because of the low thermal conductivity of the oil phase, the column diameter must be limited in order to avoid an excessively high radial temperature gradient cf. H. K. Latourette et al., J. Am. Oil Chem. s.: 37 (1960).